RERUN: Canada's National Tree

Since today is Canada Day, I figured I should either do a post that has to do with this great country, or at the very least re-post the blog I did last year on this day. Last year's blog it is! A new blog post continuing the "Sandra's Garden" theme will be coming shortly. To keep you tied over until then, enjoy this post from Canada Day last year about the differences between sugar maples (our National tree) and Norway maples (an invasive species). Happy Dominion Day!

Species names: Acer saccharum, Acer platanoides

Common names: Sugar maple, Norway maple

Location: Ontario

Since one of these trees is native and the other is not, and there's a reason why one would be featured more prominently over the other on a wonderful day such as today, I put up the photo for a native species.

Since today is Canada Day, I figured I should probably feature our national tree, the one proudly flown every day on our flag, the sugar maple (a species that I didn't quite do justice to in this blog post). Unfortunately, the Norway maple has become almost as common as the sugar maple in Canada (if not more common in some areas) because it is, for some obscure reason, planted in preference over our native species. Perhaps it's because it doesn't succumb to the native sugar maple pests that we have, but it was also the reason why we have periodic outbreaks of the Asian longhorned beetle, its primary pest, which is decimating forests across the country. The other downside of the Norway maple is that it produces phytochemicals from its roots that deter understory growth (including grass, if you choose to plant one in your front yard), and when fully mature it can inhibit the growth of native species of trees and shrubs in a forest to such an extent that you sometimes find "Norway maple oases" where nothing else exists.

So how can you tell the difference between a native sugar maple and an invasive, non-native Norway maple? The key is in the leaves. First, if you've got a purple maple tree in your front yard you've got a Norway maple. Sugar maples have never been bred to have purple leaves, so that's a great place to start to be able to stay away from the Norway maple. Second, take a look at the lobes of the leaf, specifically the top lobe. Does it have deep groves running almost halfway down the leaf, separating the top lobe from the ones on each side of it? Or is the lobe very shallowly separated from the rest of the leaf? Shallow lobes are Norway maple leaves, deep lobes are sugar maple leaves. If you look at the second picture (sugar maple on the left, Norway maple on the right), you can also see that when you compare them side-by-side the number of teeth along the leaf's edge also differs quite a bit; the Norway maple has quite a few more teeth along each lobe where the sugar maple doesn't. Third, take a look at where the petiole (or the "leaf stalk") branches off into the main veins of the leaf. Are these veins approximately the same colour as the tissue of the leaf, or is there a drastic difference in colour? As in the third picture, veins roughly the same colour as the leaf is seen in the sugar maple, drastically different leaf main vein colouring is characteristic of the Norway maple. The last and most easy method for telling the two species apart is by breaking a leaf off the stem and looking to see what happens. Is there a white milky latex that oozes out of the petiole? Or is the base of the petiole dry? The Norway maple is the one producing latex, the sugar maple doesn't (and that latex can be irritating to the skin, so be careful!).

Now you know how to tell the two trees apart. And not to leave out my American friends, the sugar maple is also the state tree of New York, West Virginia, Vermont and Wisconsin. All four of those states have impeccable taste in trees! :)

Happy Canada Day!

Dear Europeans: please take your buckthorn back!

Species name: Rhamnus cathartica

Common name: European buckthorn, common buckthorn

Location: Ontario

The European buckthorn is native to (you guessed it) Europe, but also north Africa, and all the way east towards western Asia. It was introduced to North America in the early 1800s, and has since become a menace. The fruit start as green unripe berries, turn a pinkish-red (if you catch them that way; that colour doesn't last long), then a very dark black. These are a favourite fruit of birds, and it turns their poop an awful black-purple colour that is an absolute disaster to get off a white car. Interestingly enough, buckthorn seeds require the digestive and abrasive action of a bird's "waste management system" in order to germinate; unlike many tropical plant species that require the same germination mechanism, it can be any bird species. This shrub (or sometimes tree, depending on how much light and space it is given) is a great example of the idea that just because a bird can eat it doesn't mean a human can; the berries have a very strong laxative effect, and if enough are eaten they can cause severe dehydration (an effect that was exploited in the 18th and 19th centuries medicinally; it is no longer used for this purpose).

A couple of years ago the City of London did a tree survey based on aerial images and citizen reporting, to determine not only the percent cover of trees in London, but also the species of tree. I still don't quite understand how this worked with aerial images, since the resolution can only be so good; apparently they used some sort of combination of infra-red, ultra-violet, and true colour images to get a rough estimation of the species of tree. Sometimes the actual species could be distinguished, other times it was a vague common name like "oak tree" (which could apply to about 15 different species, some native and some not). The results were shocking, and yet they don't seem to have had any impact on species planted by the City. The top "tree", by leaf cover and by number of individuals, was the buckthorn (this is probably both glossy buckthorn and common buckthorn). The next tree was the Norway maple, another non-native and invasive species, and the tree rounding up the top three was either the sugar maple (number of individuals), or the black walnut (leaf area). Despite most of the trees in London being non-native and invasive species, there were two trees planted on my street this summer because of the ash tree purge (nothing like cutting down a native North American, healthy tree to replace it with a non-native invasive species): Norway maple and American elm (which will likely either succumb to the Dutch Elm Disease, or die from salt exposure; they are not salt-tolerant and so don't serve well as boulevard trees in a cold-temperate climate!). I still don't understand why we can't start planting trees that are not only native to our area, but also suitable for the given habitat. I can't possibly see how they're too expensive; you go out into a forest, collect some seeds, and put them into soil in a greenhouse. Free trees!

If the fact that buckthorns are invasive wasn't enough, to add to that they're also the alternate host for some of North America's most devastating agricultural diseases. They harbor the soybean rust and crown rust of cereals during the winter, and when the new crops are mature enough the fungi "jump hosts" and infect a new round of plants. While the soybean rust is not a huge problem in Canada (not yet, at least; it is being tracked by Agriculture and Agri-Foods Canada and is moving further and further north every year), it can be devastating for fields in the southern United States, leading to up to 70% crop loss in a single year.

Moral of the story: if you see a buckthorn in North America, grab a hacksaw and cut it down. Or you could do as was suggested to me by a friend and naturalist: "roundup vaccinations". Drill a bunch of holes in the trunk, and spray roundup in each hole. Act baffled when it dies later that season and has to be removed. Then suggest native species to be planted in that location instead!

The blackest of the walnuts

Species name: Juglans nigra

Common name: Black walnut

Location: Ontario

This tree was once incredibly rare in Canada, but now is starting to bounce back in population numbers due to the planting of ornamental specimens. The black walnut is native to the Carolinian Forest, which extends from the Carolinas northward to southwestern Ontario. The black walnut is now relatively common in British Columbia for its attractiveness as an ornamental species, but also its value as a lumber tree.

Black walnut has been used for centuries as one of the most valuable lumber trees in North America. Since these trees have one main trunk (unlike many oak species which tend to fork after about 40 or 50 years) that is usually incredibly straight, they make very long boards suitable for furniture building. At one time, walnut was even used as a siding for houses and as material to build decks. Not a smart use since it isn't as resistant to decay like a gymnosperm wood would be (like pine or cedar), and incredibly expensive! Since the grain and colour of the wood is so attractive, the wood is so easily worked, and the wood is not very likely to bend or warp when used indoors, the prices for black walnut wood soared in the late 1800s and early 1900s. Getting a piece of furniture made of solid walnut is rare today, and would cost thousands of dollars. It is much more common to have furniture made out of a wood like oak (or, worse yet, particleboard or plywood) and either veneered or stained to look like walnut. Sometimes, too, only the exterior parts of a piece of furniture will be made out of walnut, and all of the "guts" of the piece, the parts you can't see, will be made out of a much cheaper wood.

The black walnut is a great example of a tree with a compound leaf. It is by far not the most impressive example, either in Canada or around the world, but it has a very distinctive leaf that is easily identified. If you look at the third picture down, you can see where the petiole of the leaf (the green "leaf stalk" onto which all of the leaflets are attached) is swollen at the base and wraps almost all the way around the branch that it's attached to. There is a very similar and closely related species of tree in Canada, the butternut (also called the white walnut) that has one major characteristic of the leaves that is different from the black walnut. If you look at the end of the leaf, you'll notice that there's no terminal leaflet in the black walnut (sometimes there is, but it is never the same size as the rest of the leaflets). The butternut always has a terminal leaflet, and it's always at least the same size (sometimes bigger) as the rest of the leaflets.

Yes, the walnuts you buy at the store are the fruit of this tree! The best way to harvest them is to pull them off the tree when the fruit is still green and unripe since that's when the flesh on the inside tastes best. The green outer husk is incredibly difficult to remove (just sit and listen to a squirrel trying to get inside a walnut!), and the best and easiest way is to run over the fruit with an SUV. I'm not kidding! Line them up on the driveway or in a parking lot, and give it a go! Once the outer husk is removed, the nut on the inside (with the hard shell that's sold in grocery stores as "in-shell walnuts") will start to look familiar. Take a nut-craker, crack open the outer shell and enjoy! They don't need to be roasted in the oven first, but some people enjoy them more that way. Unfortunately, what's sold most often in grocery stores is the Persian walnut which is much easier to harvest (and probably accounts for its higher popularity). This is causing more and more Persian walnut trees to be planted in favour of the native species, which is always a downside of agriculture! A word of caution: if you're going to harvest your own black walnut nuts, make sure you wear gloves! Anyone who has seen the remnants of squirrels gnawing their way through a walnut on the sidewalk knows just how potent the dye from the husk, made up of juglone, plumbagin and tannins, can be! It will permanently dye your hands for weeks, and was actually often used as a permanent hair dye (and sometimes still is in "natural beauty products").

One downside of having black walnut in your yard is the fact that walnuts produce juglone in all of their tissues, including the roots. This chemical prevents the growth of most species of plants (and is incredibly toxic to some animals), so under most black walnut trees is a "dead zone" where nothing grows. This chemical is so potent that even black walnut seedlings, who can produce the chemical themselves, are sensitive to it and will die! This phenomenon is referred to as allelopathy, and one of the species I've already talked about, Norway Maple, is another good example of an allelopathic plant. Another good reason to wear gloves when harvesting walnuts is that some people are sensitive to juglone on their skin and it can cause an itchy rash (but the rash doesn't last as long as the dye on your hands does!).

Canada's National Tree

Species names: Acer saccharum, Acer platanoides

Common names: Sugar maple, Norway maple

Location: Ontario

Since one of these trees is native and the other is not, and there's a reason why one would be featured more prominently over the other on a wonderful day such as today, I put up the photo for a native species.

Since today is Canada Day, I figured I should probably feature our national tree, the one proudly flown every day on our flag, the sugar maple (a species that I didn't quite do justice to in this blog post). Unfortunately, the Norway maple has become almost as common as the sugar maple in Canada (if not more common in some areas) because it is, for some obscure reason, planted in preference over our native species. Perhaps it's because it doesn't succumb to the native sugar maple pests that we have, but it was also the reason why we have periodic outbreaks of the Asian longhorned beetle, its primary pest, which is decimating forests across the country. The other downside of the Norway maple is that it produces phytochemicals from its roots that deter understory growth (including grass, if you choose to plant one in your front yard), and when fully mature it can inhibit the growth of native species of trees and shrubs in a forest to such an extent that you sometimes find "Norway maple oases" where nothing else exists.

So how can you tell the difference between a native sugar maple and an invasive, non-native Norway maple? The key is in the leaves. First, if you've got a purple maple tree in your front yard you've got a Norway maple. Sugar maples have never been bred to have purple leaves, so that's a great place to start to be able to stay away from the Norway maple. Second, take a look at the lobes of the leaf, specifically the top lobe. Does it have deep groves running almost halfway down the leaf, separating the top lobe from the ones on each side of it? Or is the lobe very shallowly separated from the rest of the leaf? Shallow lobes are Norway maple leaves, deep lobes are sugar maple leaves. If you look at the second picture (sugar maple on the left, Norway maple on the right), you can also see that when you compare them side-by-side the number of teeth along the leaf's edge also differs quite a bit; the Norway maple has quite a few more teeth along each lobe where the sugar maple doesn't. Third, take a look at where the petiole (or the "leaf stalk") branches off into the main veins of the leaf. Are these veins approximately the same colour as the tissue of the leaf, or is there a drastic difference in colour? As in the third picture, veins roughly the same colour as the leaf is seen in the sugar maple, drastically different leaf main vein colouring is characteristic of the Norway maple. The last and most easy method for telling the two species apart is by breaking a leaf off the stem and looking to see what happens. Is there a white milky latex that oozes out of the petiole? Or is the base of the petiole dry? The Norway maple is the one producing latex, the sugar maple doesn't (and that latex can be irritating to the skin, so be careful!).

Now you know how to tell the two trees apart. And not to leave out my American friends, the sugar maple is also the state tree of New York, West Virginia, Vermont and Wisconsin. All four of those states have impeccable taste in trees! :)

Happy Canada Day!